Journal ArticleDOI
Second-order scalar-tensor field equations in a four-dimensional space
TLDR
In this article, the second-order Euler-Lagrange tensors are derived from a Lagrangian which is at most of second order in the derivatives of the field functions.Abstract:
Lagrange scalar densities which are concomitants of a pseudo-Riemannian metric-tensor, a scalar field and their derivatives of arbitrary order are considered. The most general second-order Euler-Lagrange tensors derivable from such a Lagrangian in a four-dimensional space are constructed, and it is shown that these Euler-Lagrange tensors may be obtained from a Lagrangian which is at most of second order in the derivatives of the field functions.read more
Citations
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Nanohertz gravitational waves from a null-energy-condition violation in the early universe
TL;DR: In this article, the null energy condition (NEC) violation admits accelerated expansion with the scale factor $a\ensuremath{\propto}(\ensurem{-}t{)}^{\ensure m{-p}$ ($pg0$), which gives the tensor spectral index ${n}_{t}=2/(p+1)g0$, which is consistent with the NANOGrav result.
Journal ArticleDOI
Do cosmological data rule out f(R) with w≠−1?
TL;DR: In this article, the Equation of State (EoS) approach is applied to dark sector perturbations and applied to $f(\mathcal{R})$ gravity models of dark energy.
Journal ArticleDOI
Reheating predictions in gravity theories with derivative coupling
TL;DR: In this paper, the authors investigate the effects of the non-minimal derivative coupling (NMDC) on the CMB observables by taking into account both the dynamics of the inflationary slow-roll phase and the subsequent reheating.
Journal ArticleDOI
Direct detection of dark energy: the XENON1T excess and future prospects
Sunny Vagnozzi,Luca Visinelli,Luca Visinelli,Luca Visinelli,Philippe Brax,Anne-Christine Davis,Jeremy Sakstein +6 more
TL;DR: In this paper, the authors explore the prospect for direct detection of dark energy by current and upcoming terrestrial dark matter direct detection experiments, and examine whether the electron recoil excess recently reported by the XENON1T collaboration can be explained by chameleon-screened dark energy, and find that such a model is preferred over the background-only hypothesis at the $2.0 ε-ensuremath{sigma} level, in a large range of parameter space not excluded by stellar (or other) probes.
Journal ArticleDOI
Axial quasinormal modes of static neutron stars in the nonminimal derivative coupling sector of Horndeski gravity: Spectrum and universal relations for realistic equations of state
TL;DR: In this paper, the axial quasinormal modes of static neutron stars in the nonminimal derivative coupling sector of Horndeski theory were analyzed for ten different equations of state with different matter content.
References
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Journal ArticleDOI
Mach's principle and a relativistic theory of gravitation
Carl H. Brans,R. H. Dicke +1 more
TL;DR: In this paper, the role of Mach's principle in physics is discussed in relation to the equivalence principle and the difficulties encountered in attempting to incorporate Mach's principles into general relativity are discussed.
Journal ArticleDOI
The Einstein Tensor and Its Generalizations
TL;DR: In this paper, the number of independent tensors of this type depends crucially on the dimension of the space, and, in the four dimensional case, the only tensors with these properties are the metric and the Einstein tensors.
Journal ArticleDOI
Comments on the scalar-tensor theory
TL;DR: In this article, the ponderomotive laws of a scalar-tensor theory are constructed free of approximations in the form of integral laws, and the integrals are extended over two-and three-dimensional domains that lie entirely in empty space but surround the regions containing matter.
Journal ArticleDOI
The uniqueness of the einstein field equations in a four-dimensional space.
TL;DR: In this article, the Euler-Lagrange equations corresponding to a Lagrange density which is a function of g ≥ 2 and its first two derivatives are investigated and necessary and sufficient conditions for these equations to be of second order are obtained and it is shown that in a four-dimensional space the Einstein field equations (with cosmological term) are the only permissible second order Euler Lagrange equations.
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